Method of making electroluminescent display devices having etched character electrodes

ABSTRACT

An electroluminescent display device is provided, in which a substrate of the display is comprised of character electrodes, external connecting means for facilitating connections to external apparatus and a plurality of interconnecting means between the character electrodes and external connecting means. The character electrodes, interconnecting means and external connecting means form one integral unit, with the display device itself being a monolithic structure.

United States Patent I Boucher [4 1 Apr. 25, 1972 1541 METHOD OF MAKING [56] References Cited ELECTROLUMINESCENT DISPLAY UMTED STATES PATENTS DEVICES HAVING ETCHED 3,235,938 2/1966 Greene ..29/25.l6 CHARACTER ELECTRODES 3,289,198 11/1966 Dickson, Jr. et al. ..3l5/169 72 I t I G ald B h H d 3,315,248 4/1967 Benn CI 3.1 ..3l3/l09.5 X l 1 3,384,770 5/1968 Vodjka ..313/109.s x [73] Assignee: Sanders Associates Inc.,,Nashua, NH. 3,385,992 5/1968 Chaberski. ..3l5/ 169 X 1 3,435,270 3/1969 Vodika ..313/109.5 X [22] Filed: June 12, 1970 Prima Examiner-John F. Cam hell 1 7 ry p [2 1 No 5785 Assistant Examiner-Richard Bernard Lazarus Related U.S. Application Data A! "0- Ethngel' [62] Division of Ser. No. 731,191, May, 1968, Pat. No. [57] ABSTRACT An electroluminescent display device is provided, in which a substrate of the display is comprised of character electrodes, [52] U.S. Cl ..29/25.l6, 29/2511 external connecting means for facilitating connections to [51] int. Cl. ..H0lj 9/18, H01 9/36 ternal} apparatus and a plurality of interconnecting means Field Search 251.2511, between the character electrodes and external connecting means. The character electrodes, interconnecting means and external connecting means form one integral unit, with the display device itself being 'a monolithic structure.

4 Claims, 3 Drawing Figures PATENTEDAPR 2 5 I972 FIG, I

INVENTOR GERALD BOUCHER aw FIG. 5

AGENT FIELD OF THE INVENTION THE PRIOR ART In the field of electroluminescent display assemblies, it is conventional practice to make the exterior glass or other transparent material the substrate of the display. Such substrates, while rigid, provide a display that is heavy and relatively fragile. In completing the structure of these conventional displays, a tin oxide coating or any other light-transmitting electrically conductive material is applied to one surface of the glass plate thus forming the transparent electrode. An electroluminescent phosphor layer which may be comprised of a dielectric material such as glass or plastic having dispersed therein particles of an electric field responsive phosphor is placed adjacent the transparent electrode. The dielectric material and the phosphor can be applied as separate layers. A metallic configuration electrode or character electrode composed of steel, aluminum, gold, copper, or other electrically conducting material is bonded to the electroluminescent phosphor layer. The metallic configuration electrodes may be used as the backing surface of the display or a layer of dielectric material may be laminated to the electrode surface.

In the operation of devices such as described above, an electrical potential is applied between the metallic configuration electrode and the transparent electrode creating an electric field across the phosphor layer, thus, producing visible light which identifies the characters to be displayed. In order to apply this power, electrical connections must be made to the transparent electrode and the character electrode(s).

This requirement necessitates that electrical connections be made to very thin metallic electrodes. From a manufacturing viewpoint, the task of making relatively fragile electrical connections coupled with the relative weakness of the electroluminescent displays, because a glass surface is used as the substrate, presents many problems.

The solution to the problem of providing solid electrical connections to the character electrodes lies in forming a substrate in which the character electrodes and interconnecting means are an integral part thereof. In providing such a substrate, the relative weakness of the is if also eliminated because the outer glass surface no longer fulfills this function.

SUMMARY OF THE INVENTION From the foregoing, it will be understood that among the objects of this invention are the following:

To provide an electroluminescent display in which the character electrode pattern, the insulating material, and the interconnecting conductive members provide a rugged substrate for the phosphor layer and the transparent electrode;

To provide an electroluminescent display which is light in weight, compact, rugged and more reliable than heretofore available;

To provide an electroluminescent display in which the use of soldered joints or conductive cement between the electrode segments and the electrical connection leads are eliminated;

To provide an electroluminescent display in which the bonding of .the individual electrode areas to the electroluminescent phosphor layer is eliminated;

To provide an electroluminescent display that is relatively free of productionproblems and is inexpensive to manufacture;

To provide an electroluminescent display in which the electrode patterns, the transparent electrode, the electroluminescent phosphor layer, and the interconnecting conductive members to the external electronic circuits form a monolithic structure.

In accordance with this invention, these objectives are achieved by forming the character electrodes and electrical interconnecting circuits thereto as an integral component of the substrate of the electroluminescent display. That is, the character electrodes, the electrical circuit paths within the substrate and the conductive members which extend through the insulative material that surrounds and separates the character electrodes and the circuit paths are molecular-1y united without the necessity of soldering or the like when formed by a printed circuit process, and form an integral unit. In this manner, the passive elements of the display are formed as part of the substrate which supports the active elements of the display and thereby provide a durable, rugged display.

For a clearer understanding of the nature and objects of my invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of various types of character electrodes;

FIG. 2 is a partial perspective view of the character electrodes, and their associated printed circuit interconnecting means, and

FIG. 3 is a cross-sectional view of a complete electroluminescent display.

It will be understood that these figures present an enlarged view of the electroluminescent display for clarity and illustration purposes only. The dimensions of a finished display are greatly reduced in surface area and depth. Also, the number of character electrodes, the number of conductive members between circuit levels, and the number of associated electrical interconnecting circuit paths and terminals have been limited for illustration purposes only. Description of the Preferred Embodiment Referring now to FIG. 1, there is shown an electroluminescent display having various types of preformed permanent character electrodes 12 (a-e) comprising various symbols, designs, etc.

It is apparentfrom an examination of the characters 12 (a-e) that the actual character configuration which can be formed is unlimited. Any shape or pattern .may be produced by a printed circuit process thereby providing numerous applications for this display. For example, the electrode segments may be formed into a circular pattern 12a whereby the radial segments can represent, for example, a meter dial or the hands of a clock. The character electrode 12b represents a letter of the alphabet. A seven-segment presentation is illustrated by 12c such that any illuminated number from zero to nine may be produced by energizing the proper segments. A i l-segment presentation 12d, can with proper energization of the segments, provide any number or letter of the alphabet. Likewise, a seven-segment or fraction presentation 12e is employed to provide illuminated numerical digits whether as a fraction or as a value in tenths. These configurations are shown by way of example only. In addition, substrate 11, as will be subsequently explained, includes connection means 13 to connect the permanent character electrodes 12 (a'e) to external apparatus. Connection means 13 may consist of eyelets, protruding pins or other known methods or combinations thereof to provide an electrical connection for external apparatus.

Referring now toFlG. 2, there isshown a partial electroluminescent display (substrate 11) showing the character electrodes, associated printed circuits, and interconnecting means. a

The method of construction of substrate 11 may vary as to the initial steps depending upon the type of connection means 13 used to facilitate connections to external apparatus. In any event, the methods by which connection means 13 are incorporated as part of substrate 11 are well known in the art.

The formation of the substrate 11 starts with a sheet of copper (to be formed into pillars or lands l4 and circuit paths 16) that is preferably thick enough such that operations may be performed on it without the need of a supporting device.

The copper sheet is thoroughly cleaned, coated with a light sensitive resist, dried and covered with a film mask which locates the upstanding conductive members or lands 14. The copper layer is then exposed to light (preferably ultraviolet), developed, rinsed, dried, dyed if desired, dried and touched up. and etched to a predetermined controlled depth to form the desired upstanding portions or lands. The surface is then 1 flushed, dried and the exposed resist removed. It is then again rinsed and dried. A layer of epoxy filter glass 15 or other insulating material is laminated over and surrounding the upstanding conductive members or lands 14. The surface of the insulating material 15 is then sanded, ground, or otherwise thinned down to remove the excess epoxy to leave the uppermost surface of the lands l4 exposed and cleaned. This method for providing lands 14 is similar to that set forth with more particularity in my US. Pat. No. 3,374,129, assigned to the asslgnee of this application. The surfaces of the lands 14 will be moiielcularly united tothe character electrodes 12 of FIGS. 1 an The opposing surface of the sheet of copper 10 is resist coated, washed, exposed to light, developed, rinsed, dried, dyed if desired, dried and touched up, and etched to form'an appropriate printed circuit layer 16. This surface is then cleaned and a layer of epoxy fiber glass 17 or other insulating material is laminated thereover.

The surface of the laminate with the exposed conducting members or lands 14 is then cleaned, and activated by being dipped in hydrocloric acid, dipped in a suitable catalyst, rinsed, dipped in a copper mix solution, dipped in fluoboric acid, electroplated with copper to form a layer rinsed and dried. The copper layer which will be formed into the character electrodes 12, is then cleaned, coated with a light sensitive resist, dried and covered with a film mask to locate the permanent electrode characters. This copper layer is then exposed to light, developed, rinsed, dried, dyed if desired, dried and touched up, and etched to form the desired patterns which are the second or permanent electrode characters, such as electrode segment [2e illustrated in FIG. 2.

Note that since the character electrodes 12 are made by a printed circuit process, the electrodes may be formed into any form imaginable and, therefore, the use of the display is almost without limit.

The electrode segments 12 (a-e) in this embodiment are located within the same plane and, therefore, spacing therebetween is selected to minimize any tendency for an electrical-breakdown. To insure against an electrical breakdown between the electrode segments, a layer of insulative material may be placed around and over the electrodes and the surface then ground, sanded or otherwise thinned down to expose the uppermost surface of the electrode segments 12. A base is thereby provided to which is applied a uniform layer of phosphor material (not shown in FIG. 2). A uniform layer of phosphor material ensures that each character is illuminated with the samedegree of brightness.

By utilizing the method, herein described, for producing the interconnecting printed circuits 16 it is possible that each character electrode 12 may have a multiple of interconnection contacts. For example, segment (a) of the characterelectrode 12c, FIG. 2, may be integrally connected by a multiple of necting means 13. Although not illustrated, the printed circuit leads may be interconnected between segments of various character electrodes. For example, if the display was to present certain combinations of letters or numbers then the letters could be interconnected such that only one circuit path needs to be connected to only one external connecting means 13. In this manner, the same character electrode may be shared by more than one external system thereby increasing its usefulness. The connecting means 13 may be eyelets which extend through the electroluminescent panel, illustrated as 13b, FIG. 2 or the connecting means 13 may be eyelets which only appear on one side of the electroluminescent panel such as 13a, FIG. 2. In any event, the method of inserting these eyelets is well known.

The above-described construction is very rugged, durable, and capable of withstanding excessive external forces without any danger of interrupting the electrical circuits between the connection means 13 and the character electrodes 12. There is little danger that one of the character electrodes 12 be separate from a phosphor layer which has been applied to the electrodes. Thus, the electroluminescent display described herein attains the goals set forth in the objects of the invention.

The embodiment of the invention described herein has one circuit layer 16 beneath the permanent character electrode 12. This concept, however, is not limited to any particular number of printed circuit levels, for as many levels may be ftigned as deemed necessary by following the steps outlined a ve.

Although the electrical connection means 13 for the electroluminescent display are illustrated as surrounding the electrode segment (see 120 of FIG. 1) or positioned along the perimeter of the display device (see l2b-l2c, FIG. 1), 10 their placement is not restricted to these two locations, but will depend on the associated interconnecting leads to the electrical apparatus. Also, the connection means 13 is not restricted to protruding pins or eyelet ypes. but, for example, may be in the shape of an exposed tab or anyother known means. The connection means 13, however, do not extend through or come in contact with the dielectric layer 21, phosphor layer 22, transparent electrode 23, or the cover coating 25 (see FIG. 3). If the connection means 13 should come in contact with the transparent electrode 23 in particle, then a direct electrical circuit would exist between the transparent electrode 23 and the character electrodes 12 and the phosphor layer would not luminesce.

Referring now to FIG. 3, there is illustrated a .complete structure of an electroluminescent display device 20. A'dielectric breakdown layer 21 of barium titanate intermixed with a dielectric resin binder is applied over the layer of character electrodes 12. Adjacent to and above the dielectric breakdown layer 21, a phosphor layer 22 is applied by any suitable process, such as by spraying, silk screening or other known methods. The phosphor layer 22 comprises any electroluminescent phosphor material in which the phosphors are energizable by electric fields to produce visible. light, and accordingly are termed field responsive." As a specific example, the electroluminescent material may comprise zinc sulfide activated by copper and coactivated by chlorine, but any other suitable electroluminescent material may be substituted therefor. The phosphor may also be intennixed with a suitable light-transmitting dielectric material.

Adjacent to thephosphor layer is the first electrode 23. The first electrode 23 consists of a thin, light-transmitting electrically conducting material which is coated as a thin film on a fibrous glass sheet or other vitreous body by, for example, iridizing. An example of suitable materials employed are tin oxide, stannic oxide, or indium oxide. The transparent electrically conductive layer 23 usually is one sheet covering 'all of the character electrodes l2'but, if necessary, it may be applied in sections such as to cover each character electrode individually. A conductive lead 24, FIG. 3, is bonded to the printed circuit leads l8 and 19 to more than one external conlight-permeable, electrically conductive electrode. This lead is made available for connection to an external power source through a connection means (not shown), for. example, a tab may be soldered thereto and brought out from the body of the display. A voltage potential, applied between the transparent electrode and any one character electrode 12, causes the associated phosphor material to luminesce, thereby illuminating the display 20. The connection to the character electrode 12 is made at a connection means 13 (not illustrated in this FIG.) as shown in FlG.'2. Where it is necessary to protect the panel from the effects of the atmosphere such as moisture or dust, the transparent electrode 23 and surrounding areas, if any, may be covered with a layer 25 of transparentplastic glass or other suitable bondable material.

While the instant display device is not limited in the size in which it can be fabricated, it is particularly adapted for small displays. The compactness of the display has as its practical limitation the observers ability to visually perceive and distinguish the characters of the display while the largeness of the display area is guided by practical considerations. Another advantage of my invention is the wafer-thin thickness of the display. This thinness makes the display device particularly adaptable for use in areas where relatively bulky displays present design packaging problems.

The operation of the electroluminescent displays is carried out according to methods known in the art; that is, any one of the character electrodes 12 or combination of character electrodes 12 may be energized to illuminate the electroluminescent display device 20. This is done by applying a voltage potential between the transparent electrode 23 at conductive lead 24, and any one or combination of character electrodes 12.

It will be appreciated from the foregoing description that the electroluminescent display of this invention has efficiently attained the objectives previously set forth. That is, the external connection means 13, the circuit layer 16, the upstanding conductive members or lands l4, and the character electrode segments 12 are molecularly united so as to form one integral electrical circuit; and this integral structure combined with the insulative material which is formed around the electrical elements and is flush with the uppermost surface of the character electrodes 12 provides a very durable, rugged substrate for the display device that is not present when a piece of transparent glass is used as the substrate. In addition, a display device produced by this method is wafer-thin in size and light in weight permitting usage where these factors are important. Also, it is apparent that my invention provides a simplified and economical construction of a monolithic electroluminescent display.

This invention has been described in conjunction with preformed characters which display numbers, letters, or simple designs. But, it is seen that by extending the concept of using multiple interconnecting printed circuits paths, one can develop a system which when used with an appropriate electronic coding circuits will produce phrases, words, animated cartoons, or moving displays. Thus, the potential applications of this type of display are unlimited. Thus, while the abovedescription relates to specific principles of this invention, it is to be understood that this description is made only by way of example and not as a limitation thereon, for one skilled in the art may make modification thereto, but still be within the true spirit and scope of this invention as set forth in the appended claims.

What I claim:

l. The process of producing an electroluminescent display device starting with a first sheet of a metallic conductor of sufficient thickness to be capable of self-support and comprising the steps of:

producing on a first surface of said sheet an image of desired interconnecting members,

etching away to a predetermined depth the undesired conductor leaving projecting interconnecting members, applying to the etched surface a layer of insulating material and removing a rtion of said insulating material down to the upperrnos level of said interconnecting members so as to expose the uppermost surface thereof,

applying a second sheet of metallic conductor over said insulating material so as to unite with said exposed interconnecting members,

etching away undesired conductor from the other surface of said first conductive sheets to form a desired printed circuit,

etching away undesired conductor from the exposed surface of said second conductive sheet to form character electrodes, whereby selected ones of said character electrodes and portions of said printed circuit are interconnected by said interconnecting members,

applying to said character electrodes a layer of electroluminescent phosphor,

applying to said electroluminescent phosphor layer a transparent, electrically conductive layer.

2. The process claimed in claim 1, further including the step of applying a layer of dielectric material between said character electrodes and said phosphor layer.

3. The process claimed in claim 1, further including the step of applying a transparent, protective coating over said transparent electrically conductive layer.

4. The process claimed in claim 1, further including the step of forming terminal means with said display device connected to said printed circuit and said transparent electrically conductive layer, said terminals being employed for facilitating external connection tosaid display device. 

1. The process of producing an electroluminescent display device starting with a first sheet of a metallic conductor of sufficient thickness to be capable of self-support and comprising the steps of: producing on a first surface of said sheet an image of desired interconnecting members, etching away to a predetermined depth the undesired conductor leaving projecting interconnecting members, applying to the etched surface a layer of insulating material and removing a portion of said insulating material down to the uppermost level of said interconnecting members so as to expose the uppermost surface thereof, applying a second sheet of metallic conductor over said insulating material so as to unite with said exposed interconnecting members, etching away undesired conductor from the other surface of said first conductive sheets to form a desired printed circuit, etching away undesired conductor from the exposed surface of said second conductive sheet to form character electrodes, whereby selected ones of said character electrodes and portions of said printed circuit are interconnected by said interconnecting members, applying to said character electrodes a layer of electroluminescent phosphor, applying to said electroluminescent phosphor layer a transparent, electrically conductive layer.
 2. The process claimed in claim 1, further including the step of applying a layer of dielectric material between said character electrodes and said phosphor layer.
 3. The process claimed in claim 1, further including the step of applying a transparent, protective coating over said transparent electrically conductive layer.
 4. The process claimed in claim 1, further including the step of forming terminal means with said display device connected to said printed circuit and said transparent electrically conductive layer, said terminals being employed for facilitating external connection to said display device. 